(1) Field of the Invention
The present invention relates to a photosensitive material for electrophotography, which is used in a copying machine, a laser printer and the like. More particularly, the present invention relates to a photosensitive material for electrophotography, in which rise of the surface voltage or residual voltage caused on repetition of charging and light exposure is controlled and good electrophotography characteristics are stably obtained over a long period.
(2) Description of the Related Art
In the field of photosensitive materials for electrophotography, so-called function-separated type organic photosensitive materials having laminate structure comprising a charge-generating layer (CGL) and a charge-transporting layer (CTL) have been gradually used. Single-layer dispersion type organic sensitive materials comprising a charge-generating substance dispersed in a medium of a charge-transporting substance have already been known as well as the above laminate type photosensitive materials.
A substance having a high carrier mobility is required as the charge-transporting substance for these photosensitive materials, and polymeric materials initially used, such as polyvinyl carbazole (PVC), have been replaced by low-molecular-weight compound materials used in resin dispersions. However, in view of the molding processability, it is preferred that a film-forming substance which can be used singly be used as the charge-transporting substance. The above-mentioned PVC has a film-forming property, but is defective in that the dimer site formed by adjacent carbazole rings acts as the hole carrier trap to cause reduction of the electrophotography characteristics of the the photosensitive material.
Recently, Japanese Unexamined Patent Publication No. 61-170747 proposes a photosensitive material comprising an organic polysilane as the hole-transporting material. This organic polysilane can be formed into a film from a solution, and it is known that of amorphous polymeric materials, the organic polysilane has a higher hole drift mobility (up to 10.sup.-4 cm.sup.2 /V.sec).
Not only initial characteristics but also a good stability at the repeated use is required for a photosensitive material to be loaded on a copying machine and the like, but in connection with a photosensitive material comprising the organic polysilane, this stability has not been sufficiently examined.
We made investigations with a view to applying an organic polysilane to a commercial photosensitive material for the electrophotography, and as the result, it was found that if this photosensitive material is subjected to charging-light exposure repeatedly, especially if the photosensitive material is irradiated with light containing ultraviolet rays, for example, light of a fluorescent lamp or xenon lamp, or sunbeams, the surface voltage and residual voltage of the photosensitive material rise, with the result that the density of the copied image is charged or fogging is caused.